An adaptive cruise control (ACC) system, sometimes called an autonomous, active or intelligent cruise control system, generally maintains a source vehicle at a driver-selected vehicle speed (speed control setting) until a slower moving lead vehicle is sensed ahead. If a slower moving lead vehicle is detected, the ACC system automatically switches from the speed control setting to one where the source vehicle is decelerated and accelerated in order to maintain a certain distance between it and the lead vehicle (headway control setting). Traditionally, some ACC systems could only operate above certain vehicle speeds, such as 25 mph for instance.
In order to provide a fuller range of operation, ACC systems have been developed that can operate at lower vehicle speeds, including in some instances all the way down to a complete vehicle stop. These systems are sometimes referred to as full speed range adaptive (FSRA) cruise control systems.